In quantum physics, who first proposed wave–particle duality for matter?

In quantum physics, Louis de Broglie first proposed wave–particle duality for matter. In his 1924 doctoral thesis, he suggested that particles such as electrons have an associated wavelength given by λ = h/p, where p is momentum.

De Broglie's idea extended the wave-particle behavior already proposed for light. It predicted that matter should show interference and diffraction under suitable conditions. Electron diffraction was demonstrated experimentally in 1927 by Clinton Davisson and Lester Germer, and independently by George Paget Thomson.

Matter waves do not mean that a macroscopic object visibly ripples like a water wave. The wavelength becomes extremely small when momentum is large, making wave effects difficult to observe for everyday objects. For electrons and other microscopic particles, however, wave behavior is essential for understanding atomic structure, electron microscopes, and modern quantum mechanics.